Directional couplers are used to measure RF power transmitted from RF generators to a load. In plasma processing systems, it is important to consistently obtain accurate RF power measurements of the power transmitted to the plasma processing chamber from the generator. In order to receive accurate RF power readings, geometric stability of the directional coupler is typically necessary, as well as a stable surrounding electromagnetic field. Furthermore, due to the high power levels passing through directional couplers used in plasma processing, reliable thermal interfacing with an external heat sink is also desired in order to produce consistently accurate coupler readings.